Hamburg, Germany—It was late morning when I stepped out of my hotel lobby and into the jostle of Kirchenallee Street in Hamburg's city center. I checked my watch, jotted down the time in my notebook and set out for the nearest subway station (U-Bahn in German).

The sidewalks were packed with people enjoying the glorious spring weather on May Day, a public holiday similar to Labor Day in the United States. When I arrived at a stairway beneath a large "U," I checked the time. The walk from my hotel to Hauptbahnhof Süd station had taken one minute and 30 seconds. Seven minutes later I was on a subway car speeding smoothly south.

A trip across Hamburg is like visiting the launch pad of Germany's renewable energy revolution, or Energiewende. Planners call it the "built environment," a term that includes buildings, parks and the transportation system that connects them. How a city handles these ho-hum elements determines everything from energy usage to greenhouse gas emissions to the quality of life enjoyed by residents.

Without this carefully designed platform, the Energiewende would have never left the ground. So my subway ride wasn't just a way to explore Hamburg's built environment, it was an essential part of it, starting with my short walk to the U-Bahn stop. Ninety-nine percent of Hamburg residents live within 300 meters (328 yards) of a rail or bus stop, a figure that bests any major city in Europe or the United States. It's also one of the primary reasons Hamburg was crowned European Green Capital in 2011. Germany's second largest city, which is also its busiest port, shows "how an industrial city can help lead the green revolution," as an editor at Architectural Record put it.

The success of the Hamburg model can be seen throughout Germany. According to transportation writer Eric Jaffe, 88 percent of Germans live within a kilometer (a bit over a half mile) of public transportation. The comparable figure for Americans is just 43 percent. In urban centers, writes Jaffe, Germans use public transport at nearly six times the rate of Americans. In small-to-medium-sized towns, Germans use public transportation at a rate 18 times that in similar-sized American cities.

My destination on May Day was Jenischpark, 110 acres of beautifully landscaped hills created in the late 1700s. Nine minutes after boarding the subway, the cars pulled into my first transfer point—Landungsbrücken station on the banks of the river Elbe. A quick walk from the station over a pedestrian bridge and down a flight of stairs and I was ready to catch my next ride: a two-deck ferry. My Hamburg Transport Association day-pass, which cost about $5, bought me unlimited travel on subways, light rail, commuter trains, buses and ferries. The "one ticket, one fare" concept, which links all forms of public transportation into a single network to prevent long waits between transfers, originated in Hamburg in 1965.

On the pier, a guard in a wilted blue uniform was attempting to keep the boisterous and larger-than-normal holiday crowd in line. Probably because of the crowds, I had just missed a ferry and the weary guard said the next one would arrive in 10 minutes.

I didn't really mind the delay. It was sunny and warm, and across the Elbe towering cranes were plucking 38-ton containers from the decks of some of the world's largest ships. Up river was an even more remarkable sight: Europe's largest—and greenest—inner-city development, called HafenCity. Planners say this $10 billion project along Hamburg's abandoned old harbor will nearly double the city's urban-core area, add 45,000 permanent jobs and do it in a way that is low-energy, sustainable and beautiful.

• Sustainable mobility—HafenCity's design encourages pedestrian and bicycle traffic, and discourages auto traffic. Some of Hamburg's hydrogen-powered buses will serve HafenCity. Europe's largest hydrogen filling station recently opened here, and dozens of charging units for electric cars will soon join the 100 public charging stations already in service across Hamburg.

My reverie was interrupted by the arrival of the Wolfgang Borchert, a bright yellow ferry that pulled up to the pier six minutes ahead of schedule, bringing cheers from the crowd and obvious relief to the guard who smiled as she hurried to unhook the gangway chain and allow more than 100 of us to scramble aboard.

Standing at the back of the open-air top deck as the ferry pulled out from the dock, I had an even better view of HafenCity. Just as Berlin's Reichstag was built as a harbinger of the Energiewende, Hamburg's new development contains a striking building that advances the German energy revolution. The seven-story glass and steel Unilever headquarters rises from the riverbank, the shape and size of a docked ship. The building relies mostly on the natural light streaming through windows and pouring into a central atrium. Its light bulbs are LED, which are 70 percent more efficient than conventional bulbs. With its green roof, automated blinds that block direct sunlight in the summer and a host of other features, the Unilever headquarters consumes just a quarter of the energy per square foot used by traditional office buildings.

The fast-moving ferry headed downstream, leaving HafenCity behind. Fifteen minutes and three stops later, the ferry pilot called out "Neumühlen" over the loudspeaker—my stop—and angled the bow toward the pier. I followed the crowd streaming off the ferry and headed to my next mode of transportation, just over the pedestrian walkway: a row of cheery red bicycles, each marked with a white logo saying StadtRAD (in English, CityBIKE) Hamburg.

Bikes weren't covered by my travel day-pass but I discovered they are cheap and surprisingly easy to rent. Using my cell phone, I called the toll-free number printed on each bike. The operator explained that after I paid a one-time registration fee, which I did while we spoke, my credit card would be charged $1.20 for the first hour and a few cents for each minute after that. Ten minutes after disembarking from the ferry, I was pedaling my five-speed bike down the tree-lined Elbchaussee, admiring mansions built by 19th century shipping magnates and catching occasional glimpses of the Elbe.

There were nearly as many bikes as cars on the avenue. Germans are 10 times more likely to travel by bicycle than are Americans, and far less likely to travel by car than by other means. This is in part because so many clean, modern and affordable alternatives are available. But it's also because Germany, like other European countries, uses economic disincentives—primarily in the form of taxes on gasoline and diesel fuel—to decrease congestion, discourage wasteful fuel consumption and spur automakers to design more efficient cars. With a third of Germany's greenhouse gas emissions coming from transportation, this policy has also become an important tool in fighting climate change.

The taxes also mean that gas is much more expensive in Europe. In 2011, when a gallon of unleaded gas cost $3.29 at the pump in the United States, a driver in Germany paid $7.80 for the same amount of fuel. The price was a bit lower in France ($7.64) and a bit higher in the United Kingdom ($7.83). Most of the price differential between the U.S. and European nations comes from the higher taxes, which pay for new roads and for maintaining old ones. As the late Barry Commoner pointed out, there is no such thing as a free lunch—and Americans pay a high price for keeping taxes low at the pump, specifically in crumbling road and bridges. According to the World Economic Forum, the U.S. now ranks 14th in infrastructure quality, behind most European nations. Germany ranks number three.

Traffic congestion and sprawl translate into a longer commute for Americans than for residents in any European nations except Hungary and Romania. More time behind the wheel on poorly maintained roads is a deadly combination. Compared with European countries, only Greece has a higher traffic death rate than the United States. Germany's road death rate is 42 percent lower than America's.

At a little before 2 p.m., I reached Jenischpark, which an online reviewer called "a park for lovers and nature lovers." Scores of young German couples were lying in the sun, on an archipelago of blankets in a sea of bright yellow dandelions. I stretched out on a bench beneath a maple tree and watched a container ship in the distance pushing silently upstream on the Elbe. The sun felt good on my face. I closed my eyes and for 20 minutes engaged in an Energiewende of my own.

Jenischpark is part of a chain of parks and woodland areas that covers 17 percent of Hamburg—pleasant green surprises in a heavily industrialized city. New York City has Central Park, London has the contiguous Hyde Park/Kensington Gardens, and Madrid has Buen Retiro Park. But Hamburg has no single "great" park. Instead of grandeur, the city's green spaces bring nature within reach of just about everyone, every day. Nearly 90 percent of Hamburgers live within 328 yards of one of the city's 1,460 small-to medium-size parks, a system that attracts a million visits a week.

Later that afternoon I took a ferry back upstream and watched the sinking sun glint off the windows of the buildings lining the river. When reporting on energy, it's easy to focus on the brightest and shiniest subjects, especially the newest game-changing technologies. But two less glamorous workhorses—efficiency and energy conservation—are pillars of the Energiewende.

Joachim Pfeiffer, economic policy spokesman for Germany's governing coalition, told me that he considers efficiency the key to a renewable energy future. In general, buildings account for about 70% of all electrical use. A quarter of all primary energy is used in transportation.

"Energy we don't consume is energy we do not have to produce," Pfeiffer said. "And this is the best energy of all."